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EP 1 791 212 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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15.07.2009 Bulletin 2009/29 |
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Date of filing: 28.11.2005 |
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International Patent Classification (IPC):
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Microwave filters including a capacitive coupling element
Mikrowellenfilter mit einem Kapazitivkopplungselement
Filtres de microondes avec un element de couplage capacitif
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Designated Contracting States: |
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DE FR GB |
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Date of publication of application: |
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30.05.2007 Bulletin 2007/22 |
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Proprietor: Panasonic Corporation |
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Kadoma-shi
Osaka 571-8501 (JP) |
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Inventors: |
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- Sobrido, Ramon
21335 Lüneburg (DE)
- Burger, Stefan
21400 Reinstorf (DE)
- Höft, Michael
21271 Asendorf (DE)
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Representative: UEXKÜLL & STOLBERG |
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Patentanwälte
Beselerstrasse 4 22607 Hamburg 22607 Hamburg (DE) |
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References cited: :
DE-A1- 2 640 210 US-A- 5 608 363
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US-A- 4 453 146
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- PATENT ABSTRACTS OF JAPAN vol. 014, no. 102 (E-0894), 23 February 1990 (1990-02-23)
& JP 01 305605 A (NEC CORP; others: 01), 8 December 1989 (1989-12-08)
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The present invention relates to a microwave filter comprising a plurality of coaxial
resonators, at least two adjacent coaxial resonators being electrically coupled by
a capacitive coupling element having an elongated portion and, at each end thereof,
an enlarged diameter portion, the elongated portion being held by a dielectric mounting
element which is placed in an opening cut out from an end of the wall separating the
cavities of the two resonators, the elongated portion of the capacitive coupling element
projecting into both cavities, wherein the dielectric mounting has a bore for holding
at least part of the elongated portion of the coupling element, wherein the dielectric
mounting, with the coupling element inserted into the bore, is received in the coupling
opening which is of complementary shape to the dielectric mounting to engage the latter
along its length in a press-fitting manner between two opposing side walls of the
coupling opening..
[0002] The microwave region of the electromagnetic spectrum finds widespread use in various
fields of technology. Exemplary applications include wireless communication systems,
such as mobile communication and satellite communication systems, as well as navigation
and radar technology. The growing number of microwave applications increases the possibility
of interference occurring within a system or between different systems. Therefore,
the microwave region is divided into a plurality of distinct frequency bands. To ensure,
that a particular device only communicates within the frequency band assigned to this
device, microwave filters are utilized to perform band-pass and band reject functions
during transmission and/or reception. Accordingly, the filters are used to separate
the different frequency bands and to discriminate between wanted and unwanted signal
frequencies so that the quality of the received and of the transmitted signals is
largely governed by the characteristics of the filters. Commonly, the filters have
to provide for a small bandwidth and a high filter quality.
[0003] Commonly, microwave filters include a plurality of resonators which are coupled together
in various configurations. Each resonator usually comprises a space contained within
a closed or substantially closed conducting surface. Upon suitable external excitation,
an oscillating electromagnetic field may be maintained within this space or cavity.
The resonators exhibit marked resonance effects and are characterized by the respective
resonant frequency and band-width.
[0004] One particular type of resonator regularly used to build microwave filters is known
as coaxial resonator. This resonator structure is short-circuited at one end and open
circuited at the other end, i.e. comprises a housing defining a cavity and having
a longitudinal axis, and a coaxial inner conductor electrically connected to the housing
at only one end. The housing comprises a base, from which the inner conductor extends
upwardly, and a side wall extending upwardly from the base, and in a certain distance
above the open end of the inner conductor, the housing is enclosed by a cover so that
a gap exists between one end of the inner conductor and the inner surface of the cover.
Such coaxial resonators are also referred to as combline resonators, and can essentially
be regarded as a section of coaxial transmission line that is short-circuited at one
end and capacitively loaded (open) at the other end. Microwave energy may be coupled
into the cavity by a magnetic loop antenna located near the inner conductor at the
short-circuited end of the transmission line. The free space between the top of the
inner conductor and the cover is referred to as the capacitive gap.
[0005] The easiest way to achieve coupling between the resonators is the provision of a
larger aperture in the wall between adjacent resonators which leads to magnetic coupling
between these resonators. Therefore, the main way of coupling between the resonators
is preferably realized as magnetic coupling. Nevertheless, there are also applications
in which besides magnetic coupling also electric coupling is helpful. Such cross-coupling
is helpful for improvement of the filter characteristic. The required electric coupling
between two coaxial resonators is achieved by provision of a capacitive coupling element
which may comprise an elongated portion or pin. The coupling element is held in a
dielectric mounting to avoid contact with the conductive walls of the cavities. The
mounting is placed in an opening cut out from an end of the side wall separating the
two adjacent resonators. The elongated portion or pin extends into both cavities and
provides an electric coupling. Such arrangement is for example described in
EP 0 525 416 B1.
[0006] If an increased capacitive coupling strength is desired, the coupling element is
provided with enlarged diameter end portions or disks at both ends of the elongated
pin portion. Such coupling elements are for example disclosed in
DE 21 61 792 A1 on which the preamble of claim 1 is based.
[0007] In order install such coupling elements with enlarged diameter disks at its ends,
it is known in the prior art to assemble two dielectric mounting parts around at least
part of the elongated portion of the coupling element. The two pieces when put together
form a bore in which the elongated portion of the coupling element is received. The
assembled two pieces with the coupling element received therein are then inserted
in an opening cut out in one of the walls separating the two adjacent resonators to
be coupled. Such arrangement is shown in Figures 3 and 4. The outer dimensions of
the mounting pieces 2, 4 are such that they may be press-fitted in the cut-out opening.
It is disadvantageous that two pieces 2, 4 need to be assembled in order to form a
mounting for the coupling element 3. Furthermore, it is very difficult to adjust the
capacitive coupling strength after the coupling element is mounted and the cover (not
shown) of the microwave filter 1 is closed.
[0008] Document
DE 26 40 210 A1 discloses a microwave filter comprising the feature of the preamble of claim 1. The
dielectric mounting is of essentially cubic shape with a groove on each side wall,
each groove being shaped for receiving one of the two side walls of the coupling opening.
In this manner the dielectric mounting is held in a fixed orientation in the coupling
opening in engagement with its side walls.
[0009] It is an object of the present invention to provide an microwave filter with at least
two coaxial resonators which are electrically coupled which simplifies the adjustment
of the capacitive coupling strength.
[0010] According to the present invention the dielectric mounting of the coupling element
is a cylindrical body formed in one piece of elastic material, the bore being perpendicular
to its longitudinal axis. The cylindrical body has a cut leading from one of its end
faces to the bore and merging with the bore.
[0011] Because of this cut the elongated portion of the coupling member may be pressed into
and slid through the cut. When the coupling element is pressed into the cut, the cut
is enlarged to a gap by elastic deformation of the cylindrical body. Once the elongated
portion of the coupling element has been slid through the cut it is received in the
bore, i.e. the axis of the bore lies in the plane of the cut. Then the elastic body
snaps back once the elongated portion left the cut area, and the cut is essentially
closed again.
[0012] The cylindrical mounting body, with the coupling element inserted into the bore,
is received in the coupling opening in the side wall separating the two resonators
to be coupled. This coupling opening is of complementary shape to the cylindrical
body so that it may receive the cylindrical body in a press'-fitting manner. The opposing
surfaces of the cut-out opening in the side wall thus have the shape of cylinder surface
segments. The cylindrical body is closely fitting into this cylinder segment opening.
Due to the press-fit of the cylindrical body in the cylinder segment opening, the
opposing portions of the cylinder adjacent to the cut are pressed together so that
the coupling element is secured in the bore.
[0013] Furthermore, due to the cylindrical shape of the mounting and its cylindrical seat,
it is possible to alter or to adjust the alignment of the coupling element by slightly
turning the cylindrical body in its press-fitting seat. This turning of the cylindrical
body results in a corresponding turning of the coupling element and thus changes the
location of the enlarged diameter disks within the respective cavities, so that the
capacitive coupling strength may be varied in this manner. In a particular advantageous
embodiment the cover of the microwave filter which covers the resonator cavities has
an opening in the area in which the free end face of the cylindrical body in the coupling
opening is situated. This allows to engage the cylindrical body, while the cover of
the microwave filter is in its closed stage, and to vary capacitive coupling strength
by slightly turning the cylindrical body in its seat as described above.
[0014] This is a particular advantage since this modification of the capacitive strength
may be performed in the completely assembled state of the microwave filter, i.e. with
the cover closed, whereas in the prior art the cover had to be opened in order to
allow to adjust or modify any of the capacitive couplings.
[0015] The cylindrical mounting body may for example be made of PTFE (polytetrafluor ethylene),
polyethylene, FEP (fluorinated ethylene-propylene), or PEEK (polyether etherketone).
The mounting body is simple to manufacture, because it may be cut from a rod to the
desired length, whereafter the bore is formed and a cut is applied running from one
of the end faces to the bore.
[0016] The invention is in the following described by way of examples with reference to
an embodiment shown in the drawings in which
Figure 1 is a perspective explosive view of an open microwave filter with the mounting
and coupling element removed from its seat;
Figure 2 is a view corresponding to Figure 1 with the mounting and the inserted coupling
element fitted into the coupling opening;
Figures 3 and 4 show views corresponding to Figures 1 and 2 of an arrangement of the
prior art.
[0017] Figure 1 shows a perspective view of a portion of a microwave filter comprising a
plurality of coaxial resonators, one of the resonator cavities being indicated by
1 and its inner conductor by 2. Each resonator comprises an essentially circular cavity.
The main couplings between the coaxial resonators are achieved by large apertures
3 or cut-outs in the side walls between adjacent cavities.
[0018] The electric coupling arrangement of the microwave filter of the present invention
is achieved by a cylindrical mounting body 7 which has a bore 9 through the cylinder
body extending perpendicular to the cylinder axis. This bore 9 is dimensioned to receive
the elongated or pin portion 5 of a capacitive coupling element 6. The cylindrical
mounting body 7 further has a cut 8 which leads from one of its end faces and merges
into the bore 9. This allows that, by stretching away the two cylinder portions separated
by the cut, a gap is formed which is sufficiently large to allow the pin portion 5
of the coupling element 6 to be slid through the cut 8 into the bore 9, whereafter
the elastic deformation forming the gap is released and the cut is closed. In this
state, the mounting body 7 with the inserted coupling element 6 is fitted into the
coupling opening 10 which is cut out from the upper end of the side wall separating
the adjacent cavities to be coupled. The opposing surfaces of the cut-out in the side
walls are adapted to conform to the surface of the cylindrical mounting body 7 and
are dimensioned to receive this cylindrical mounting body 7 in a press fitting manner.
This ensures that the capacitive coupling element 6 is securely held in place once
the mounting is in its press-fitting seat in the coupling opening 10. This state is
shown in Figure 2.
[0019] The cylindrical shape of the mounting body 7 together with the cylinder segment shape
of the opposing surfaces of the opening 10 with complementary shape provides for a
press-fitting seat of the mounting body 7. Nevertheless, it is possible to turn the
mounting body 7 inside the opening 10 in order to alter the direction of the coupling
element 6. Since this also alters the locations of the enlarged diameter coupling
disks 4, the capacitive coupling strength may be altered. This can also be achieved
if the cover (not shown) is already closed and fixed, if an opening is provided in
the cover in the area over the mounting body 7.
[0020] A further advantage of the cylindrical mounting body 7 is that it can be received
in openings which are formed in side walls of different thicknesses. In a side wall
of greater thickness a larger part of the cylinder surface is surrounded by the opposing
surfaces of the opening in the side wall, whereas in thinner side walls only a relatively
small part of the cylinder surface is engaged by the opposing surfaces of the opening,
whereas the radius of curvature of the opposing surfaces of the opening in the side
wall is always the same and equal to the radius of the cylinder.
1. Microwave filter comprising a plurality of coaxial resonators, at least two adjacent
coaxial resonators being electrically coupled by a capacitive coupling element (6)
having an elongated portion (5) and, at each end thereof, an enlarged diameter end
portion (4), the elongated portion being held by a dielectric mounting (7) which is
placed in a coupling opening (10) which is cut out from one end of a side wall separating
the cavities of the two resonators, the elongated portion of the capacitive coupling
element projecting into both cavities, wherein the dielectric mounting has a bore
(9) for holding at least part of the elongated portion (5) of the coupling element
(6), wherein the dielectric mounting (7), with the coupling element (6) inserted into
the bore (9), is received in the coupling opening (10) which is of complementary shape
to the dielectric mounting to engage the latter along its length in a press-fitting
manner between two opposing side walls of the coupling opening, characterized in that the dielectric mounting (7) is one piece of elastic material with a cylindrical body
shape said bore (9) being perpendicular to its cylinder axis, and that the cylindrical
body has a cut (8) leading from one of its end faces to the bore and opening into
the bore (9) wherein the elongated portion (5) is inserted into the bore (9) through
the cut (8).
2. Microwave filter according to claim 1, characterized in that the cover covering the resonators has, in the area above the opening (10) between
the two electrically coupled resonators, an opening which allows to engage the end
face of the cylindrical body (7) in order to turn the cylindrical body inside its
seat in the opening around its longitudinal axis, to thereby modify the capacitive
coupling strength provided by the capacitive coupling element.
3. Microwave filter according to claim 1 or 2, characterized in that the cylindrical body is made of an elastic material selected from the group consisting
of PTFE (polytetrafluor ethylene), Polyethylene, FEP (fluorinated ethylene-propylene),
PEEK (polyether etherketone).
1. Mikrowellenfilter mit einer Mehrzahl von Koaxialresonatoren, wobei wenigstens zwei
benachbarte Koaxialresonatoren durch ein kapazitives Kopplungselement (6) elektrisch
gekoppelt sind, das einen länglichen Bereich (5) und an jedem seiner Enden einen Endbereich
(4) mit vergrößertem Durchmesser aufweist, wobei der längliche Bereich von einem dielektrischen
Träger (7) gehalten wird, der in einer Kopplungsöffnung (10) platziert ist, die von
einem Ende aus aus einer die Hohlräume der beiden Resonatoren trennenden Seitenwand
herausgeschnitten ist, wobei der längliche Bereich des kapazitiven Kopplungselements
in beide Hohlräume hinein vorsteht, wobei der dielektrische Träger eine Bohrung (9)
zum Halten wenigstens eines Teils des länglichen Bereichs (5) des Kopplungselements
(6) aufweist, wobei der dielektrische Träger (7) mit dem in die Bohrung (9) eingesetzten
Kopplungselement (6) in der Kopplungsöffnung (10) aufgenommen ist, die eine zu dem
dielektrischen Träger komplementäre Form hat, um den letzteren entlang seiner Länge
im Presssitz zwischen den beiden gegenüberliegenden Seitenwänden der Kopplungsöffnung
einzufassen, dadurch gekennzeichnet, dass der dielektrische Träger (7) ein Stück Kunststoffmaterial mit einer zylindrischen
Körperform ist, wobei die Bohrung (9) senkrecht zur Zylinderachse liegt, und dass
der zylindrische Körper einen Einschnitt (8) hat, der von seiner Endflächen zu der
Bohrung führt und sich in die Bohrung (9) öffnet, wobei der längliche Bereich durch
den Einschnitt (8) in die Bohrung (9) eingeführt ist.
2. Mikrowellenfilter nach Anspruch 1, dadurch gekennzeichnet, dass der die Resonatoren abdeckende Deckel in dem Bereich der Öffnung (10) zwischen den
beiden elektrisch gekoppelten Resonatoren eine Öffnung hat, die es ermöglicht, an
der Endfläche des zylindrischen Körpers (7) anzugreifen, um den zylindrischen Körper
in seinem Sitz in der Öffnung um seine Längsachse zu drehen, um dadurch die von dem kapazitiven Kopplungselement bewirkte kapazitive Kopplungsstärke zu modifizieren.
3. Mikrowellenfilter nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass der zylindrische Körper aus einem elastischen Material hergestellt ist, das aus der
Gruppe bestehend aus PTFE (Polytetrafluorethylen), Polyethylen, FEP (Fluorethylenpropylen),
PEEK (Polyehteretherketon) ausgewählt ist.
1. Filtre à micro-ondes comprenant une pluralité de résonateurs coaxiaux, au moins deux
résonateurs coaxiaux adjacents étant couplés électriquement par un élément de couplage
capacitif (6) comprenant une portion allongée (5) et, à chaque extrémité, une portion
d'extrémité à diamètre agrandi (4), la portion allongée étant maintenue par un montage
diélectrique (7) placée dans une ouverture de couplage (10) qui est découpée dans
une extrémité d'une paroi latérale séparant les cavités des deux résonateurs, la portion
allongée de l'élément de couplage capacitif dépassant dans les deux cavités, dans
lequel le montage diélectrique présente un alésage (9) permettant de maintenir au
moins une partie de la portion allongée (5) de l'élément de couplage (6), dans lequel
le montage diélectrique (7) est logé, avec l'élément de couplage (6) inséré dans l'alésage
(9), dans l'ouverture de couplage (10) qui présente une forme complémentaire du montage
diélectrique afin d'engager ce dernier sur toute la longueur avec un ajustement serré
entre deux parois latérales opposées de l'ouverture de couplage, caractérisé en ce que le montage diélectrique (7) est une pièce de matériau élastique avec un corps de
forme cylindrique, ledit alésage (9) étant perpendiculaire à l'axe du cylindre et
en ce que le corps cylindrique présente une découpe (8) qui va de l'une de ses faces d'extrémité
vers l'alésage et l'ouverture dans l'alésage (9), la portion allongée (5) étant insérée
dans l'alésage (9) à travers la découpe (8).
2. Filtre à micro-ondes selon la revendication 1, caractérisé en ce que le couvercle recouvrant les résonateurs présente, dans la zone au-dessus de l'ouverture
(10) entre les deux résonateurs couplés électriquement, une ouverture permettant d'engager
la face d'extrémité du corps cylindrique (7) afin de tourner le corps cylindrique
à l'intérieur de son siège dans l'ouverture autour de son axe longitudinal, ce qui
permet de modifier l'intensité du couplage capacitif fourni par l'élément de couplage
capacitif.
3. Filtre à micro-ondes selon la revendication 1 ou 2, caractérisé en ce que le corps cylindrique est constitué d'un matériau élastique sélectionné dans le groupe
constitué du PTFE (polytétrafluoréthylène), du polyéthylène, du FEP (éthylène-propylène
fluoré), du PEEK (polyétheréthercétone).
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only.
It does not form part of the European patent document. Even though great care has
been taken in compiling the references, errors or omissions cannot be excluded and
the EPO disclaims all liability in this regard.
Patent documents cited in the description